Hello and welcome! A number of things could have gone wrong, but if you could provide more information about the position (is it always where you have photographed it, or have you moved it from elsewhere). Are these blinds kept closed or open and which hours of the day. How often do you water her? Could be overwatering, as Sally suggested, but more info is needed.

In some Native languages the term for plants translates to "those who take care of us."
Robin Wall Kimmerer

The plant is about two months old. I re-potted it the same day it was purchased. It was previously placed several feet from the windows but about a month ago I placed it near the window/door as shown in the photo below. The room is very bright on a sunny day. The plant was growing nicely but in the last month, I noticed drying/yellowing leaves. I water plant one a week. Excess water is discarded and not left in plate. I mist leaves when they appear to be drying out. I fertilize every two weeks with fish emulsion fertilizer 5-1-1. I suspected the yellowing leaves had something to do with watering but I cannot tell if it is over water or under watering.

I cannot tell the direction the window faces and whether the sun's rays fall directly on the leaves at some point during the day. If it does, then I think that is the problem.

As for watering, once a plant is repotted it makes it difficult to know when and how to water properly as watering depends on pot size, soil quality and how much the original rootball was disturbed during the repotted. I suggest that you stop fertilizing and if your tap water is hard, use distilled or filtered water instead.

Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
Contact me directly at [email protected]
I now have a book available on indoor plant care

@WillC, could it be a problem of overfertilizing, or unecessary fertilizing if I may put it another way? i think that the plants are supposed to get fertilized in spring till start of the summer months, when growth is due, not in winter? Thank you.@Delight12, I have two Dieffenbachias, they need the light, but not direct sun, which dries the plant, so if sun gets on the leaves, move it further from the window. Leave it there, where it would be cooler and go from there, see how it reacts. I hope your plant recovers!

In some Native languages the term for plants translates to "those who take care of us."
Robin Wall Kimmerer

The discolored leaves will never get any better and will probably get worse. You can either remove them entirely or try to trim off just the discolored portions. Do whatever makes it look better in your eyes. Trimming leaves will not affect the health of the plant.

Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
Contact me directly at [email protected]
I now have a book available on indoor plant care